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    <meta charset="UTF-8" />
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    <meta name="viewport" content="width=device-width, initial-scale=1.0" />
    <title>Document</title>
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  <body>
    <script>
      //   "use strict"; // 严格模式
      var a = 1,
        b,
        c;

      console.log(b); // undefined
      //   console.log(d); // is not defined
      d = 111;
      console.log(d); /// d

      d = "abc";
      console.log(d); // abc

      var a = "cc";
      console.log(a); // cc

      console.log(f);

      var f = 1;
    </script>
  </body>
</html>
